1. Field of the Invention
The present invention relates to a single-panel projection color image display apparatus, and more particularly, to a single-panel color image display apparatus having a wide color gamut and/or a high light efficiency.
2. Description of the Related Art
Color image display apparatuses of a projection type form an image by controlling a light emitted from a high-output lamp light source on a pixel-by-pixel basis using a light valve such as a liquid crystal display (LCD) or a digital micro device (DMD), and magnify and project the image using a projection optical system, thereby providing a wide screen. The color image display apparatuses of the projection type are classified into three-panel type and single-panel type according to a number of light valves.
In a general single-panel color image display apparatus, the white light irradiated from the lamp light source is separated into red, green, and blue color light beams using a color wheel, and the three colored light beams are sequentially sent to one light valve. The light valve operates according to a sequence of colors received and forms the image.
As described above, the general single-panel color image display apparatus has a simpler structure and a smaller optical system than a three-panel color image display apparatus, which forms each of the color images on three light valves using an optical separation/combination system. However, the general single-panel color image display apparatus has a light efficiency equal to ⅓ of that of the three-panel color image display apparatus due to a use of the color wheel. Hence, the single-panel color image display apparatus which includes a colored light separator having three dichroic filters and has the same light efficiency as that of a three-panel color image display apparatus has been proposed.
Referring to FIGS. 1 and 2, a conventional single-panel color image display apparatus having a dichroic filter type colored light separator includes a lamp light source 1 emitting white light, three dichroic filters 4R, 4G, and 4B which are disposed aslant with respect to one another, a micro lens array 10, and a liquid crystal display device 20.
The lamp light source 1 emits a white light in a divergent light form. The white light emitted from the lamp light source 1 is converted into a parallel light using a condenser lens 3.
The light emitted from the lamp light source 1 is separated into a red light beam R, a green light beam G, and a blue light beam B by the three dichroic filters 4R, 4G, and 4B. The dichroic filter 4R reflects the red light beam R from white light emitted from the light source 1 and transmits the remaining light beams. The dichroic filter 4G reflects the green light beam G from the remaining light beams passing through the dichroic filter 4R and transmits the remaining light beam, that is, the blue light beam B. The dichroic filter 4B reflects the blue light beam B.
Each of the three dichroic filters 4R, 4G and 4B is disposed aslant at an angle of +θ to one another. In other words, the dichroic filter 4R is disposed aslant at an angle of −θ with respect to the dichroic filter 4G, and the dichroic filter 4B is disposed aslant at an angle of +θ with respect to the dichroic filter 4G. Here, “+” indicates a counterclockwise direction, and “−” indicates a clockwise direction.
Accordingly, a chief ray of the red light beam R is incident on the micro lens array 10 at an angle of −θ with respect to a chief ray of the green light beam G, and a chief ray of the blue light beam B is incident on the micro lens array 10 at an angle of +θ with respect to the chief ray of the green light beam G.
The micro lens array 10 is formed by arranging a plurality of cylindrical lenses which form unit micro lenses 10a in a horizontal direction. The micro lens array 10 condenses the R, G, and B colored light beams, which are incident at different angles, on signal electrodes 21R, 21G, and 21B, respectively, of the liquid crystal display device 20 in a striped pattern.
The liquid crystal display device 20 has a structure in which a liquid crystal layer 23 is sandwiched between two transparent glass substrates 24 and 25. Transparent conductive films 22 and the signal electrodes 21R, 21G, and 21B are formed on both sides of the liquid crystal layer 23 in a matrix structure.
In the conventional single-panel color image display apparatus having the above structure, the R, G and B color bars, which are obtained by separating the white light into the three primary colors using the three dichroic filters 4R, 4G, and 4B and condensed on the signal electrodes 21R, 21G, and 21B of the liquid crystal display device 20, are arranged at constant intervals in the horizontal direction due to differences in the incident angles of the chief rays of the R, G, and B colored light beams, and correspond to the signal electrodes 21R, 21G, and 21B for the R, G, and B colored light beams. The R, G, and B signal electrodes 21R, 21G, and 21B are subpixels and constitute a single image pixel.
When three subpixels corresponding to three primary colors, that is, R, G, and B colors correspond to the unit micro lenses 10a and the three subpixels form the image on a screen 7 by a field lens 5 and a projection lens 6, a set of the three subpixels appears as a single image pixel.
As can be seen from FIG. 5 to be described below, when the three dichroic filters 4R, 4G, and 4B are used as the colored light separator, a reproducible color gamut is much narrower than a color gamut which can be recognized by a human eye. A color gamut indicates a range of reproducible chromaticity. Thus, a narrow color gamut is where a number of reproducible colors is few.
Accordingly, it is difficult to obtain a sufficiently wide color gamut from the dichroic filters 4R, 4G, and 4B of the conventional single-panel color image display apparatus.
Further, because the three subpixels constitute the single image pixel in the conventional single-panel color image display apparatus, the resolution of the liquid crystal display device 20 is reduced to ⅓. Accordingly, in order to realize the same resolution as the single-panel color image display apparatuses using the color wheel, a physical resolution of the liquid crystal display device 20 must be increased three times.